1. Field of the Invention
The invention relates to a memory device, and in particular to an organic non-volatile material in the active layer of the memory device.
2. Description of the Related Art
With the semiconductor industry moving toward nano-scale technology, manufacturing requirements no longer focus only on lighter weights, or thinner, shorter and smaller sizes. Moving forward, focus is also being placed on multi-function ability, mobility, multi-media ability, and network ability. Additionally, focus is also being placed on design and other customer requirements. Organic semiconductor material has benefits such as a lighter weight, lower costs, and potential for mainstream use in the future. For current organic semiconductor material, use is applied in a wide field with lower costs.
For achieving described requirements, Japanese corporations such as Rohm, NEC, Toshiba, Fujitsu, Hitachi, Matsushita have developed ferro random access memory (FeRAM). Meanwhile, IBM, Infineon, Motorola, Samsung, Toshiba, NEC, and Sony have developed magnetoresistive random access memory (MRAM). Also, Intel and ST Microelectronics have developed ovonic unified memory (OUM). Currently, the three memories are mainstream non-volatile memory (NVM) used in electronic devices. NVM may retain storage data for a hard disk and applications. For example, NVM can be applied in communication devices, computer devices, household electrical devices, and radiofrequency identification (RFID) tags. With the trend for electronic devices moving toward low energy consumption, NVM will likely increase importance in application usage.
Meanwhile, erasable programmable read only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), and flash memory technologies have been shrinking sizes of the devices toward nano-scale levels. However, due to the maturity of FeRAM and MRAM technologies reaching physical and lower cost limitations, an alternative replacement such as organic NVM (ONVM) is conceived by combining flexible electronics and NVM. For an ONVM, an organic material serves as an active layer of the NVM device. An ONVM may integrate organic materials into flexible electronics, thereby comprising a one current direction of the flexible electronic.
A major mechanism of the ONVM is a bi-stable effect, and the ONVM is an organic bi-stable diode device (OBD). For an OBD, the organic material used has low conductivity. For the device, “reading” is processed by lower voltage, and a low current signal is obtained and defined as “0”. If a higher voltage is applied, the nanoparticles mixed in the organic material would charge and become charged carriers, such that the active layer would change to have high conductivity. The voltage applying process is a so-called “write”. Note that when the applying voltage is removed, the charged carriers are stable due to memory effect. With subsequent “reading” processed by lower voltage, a high current signal is obtained and defined as “1”. The charges carried by the nanoparticles can be discharged by applying a reverse voltage, such that the active layer is converted to low conductivity. This reverse voltage applying process is a so-called “erase”. Utilizing the high and low conductivity statuses, the circle of write, read, and erase completes the methodology for memory devices.
When applied in flexible electronics, ONVM material can withstand a wet process. The ONVM is not only used in a flexible electronic carrier of the RFID, but also in all electronic devices with a memory unit to store data. The relatively more inexpensive ONVM materials may replace current NVM materials due to cost.
In U.S. Pub. No. 2004/0027849, the memory mechanism utilizes semiconductor molecules combined with metal carrier traps. It has advantages such as low driving voltage and utilization of a wet process, however, '849 still fails to prevent metal particles aggregation.
In U.S. Pub. No. 2006/0141703, Samsung provides a method for metal particles to be evenly dispersed in the active layer. This method utilizing mesoporous materials and multi-layered coating, requires a complicated process and expensive material costs.
In U.S. Pub. No. 2005/0211978, metal particles, semiconductor materials, and polymer are coupled to form a single material. In this method, the metal particles are partially grafted to the polymer chain and is not covered by the polymer.
Thus an ONVM, in which the conductive particles can be evenly dispersed in organic materials and serve as an active layer of the device is called for to improve device yield and electric properties such as retention time and endurance.